Retention is coffee left inside the grinder after a dose, and it comes out later mixed with the next one.
Why it matters
Ratio accuracy. If 1.5 g stays behind and 1.5 g of yesterday’s comes out, your dose is right by weight and wrong by composition.
Staleness. Retained grounds are stale by the next day.
Cross-contamination. Switching coffees means the first dose is a blend.
Where it hides
The chute, especially long or angled ones. The burr chamber, in the gaps around the burrs. Static-clinging grounds on every plastic surface.
How much is normal
Under 0.5 g on a grinder designed for single dosing. 1 to 3 g on a typical hopper-fed espresso grinder. 5 g or more on some bean-to-cup and older commercial grinders.
Measuring yours
Weigh 18 g of beans, grind, weigh the output. The difference is retention.
Do it twice — the second dose pushes out the first’s retention, so the numbers converge.
Reducing it
RDT — a drop of water on the beans. Kills static, which is a large part of clinging.
A bellows, puffed through the hopper after the dose. Very effective on grinders with a short path.
Tapping the grinder and running it empty for a second.
Weigh the output, not the input. This makes retention irrelevant to your ratio, which is the pragmatic fix.
By design
Single-dose grinders have short, steep paths for exactly this reason.
Last reviewed 8 August 2026